This invention relates generally to an apparatus and method for conveniently measuring impedances in a high voltage alternating current power system while minimizing operator exposure to dangerous voltage levels.
In troubleshooting a high voltage power system such as the power system of a building, it is often useful to analyze impedance characteristics, whether of a power source, load, or intermediate wiring. For reliable performance, the source impedance should be less than 1/20 the distribution and load impedances. As the source impedance increases relative to the load impedance, the voltage delivered to the load decreases and voltage waveform distortion can develop.
Prior art impedance measurement techniques are cumbersome and invasive. For example, measuring the impedance of a source requires disconnecting the source from its load and substituting an adjustable test load. Impedance is then derived from changes in source voltage resulting from varying currents drawn by the load.
Furthermore, performing the necessary voltage and current measurements in a high-voltage environment poses safety problems. If the power monitoring instrument is located adjacent to the points to be monitored, the operator is exposed to the danger of electrical shock for a long time. If the voltage probes and current clamps coupled to the necessary monitoring points are remote from the power monitoring instrument, shuttling between the instrument and probes is necessary to assure that contact has been made by the voltage probes and that the current clamps are secured in the desired orientation. Repeated visits to the monitoring points and handling of the probes and clamps increase the risk of shock. The problem is exacerbated when a multi-phase power system is to be monitored and probes or clamps may be accidentally coupled to the wrong phase.
Danger is also presented by the need to handle high-voltage connections to differential inputs at the rear of the power monitoring instrument. When struggling under protective clothing in a hot equipment closet, or in cold weather, it is easy to short phases together or to neutral with a jumper cable.
What is needed is a non-invasive apparatus and method for determining impedances of a source and load in a high-voltage power system. The apparatus and method should be convenient and should minimize operator exposure to danger of shock when performing the necessary measurements.